Some portions of documents contain information that does not change while other portions of the same document can contain information that changes quite often. For instance, a marketing firm may use a brochure for a company's particular product that should be modified to suit or target particular audiences, such as individual consumers and commercial customers. In this regard, text describing the product may stay the same while the images contained in the brochure are changed to show the product being used in a commercial setting to suit commercial customers or to show the product being used by ordinary consumers in a retail environment.
In processing documents, such as the brochures in the example above, to be rendered (e.g., printing or displaying) using a rasterizing process, for instance, all of the portions of the document are processed even though some of the portions may not have changed since it was last rendered. This needless re-processing of the same, unchanged information results in wasting processing resources.